New beast usurps T. rex as king carnivore.

In the wilds of northwestern Patagonia, they grow their dinosaurs big. Six years ago, Argentine paleontologists discovered remains of what may be the largest dinosaur ever known, a plant-eating behemoth named, appropriately, Argentinosaurus. Now, they have found the perfect counterpart: the world's largest meat-eating dinosaur.

Rodolfo A. Coria of the Carmen Funes Museum in Plaza Huincul and Leonardo Salgado of the National University of Comahue in Neuquen have named the toothy beast Giganotosaurus carolinii. The bipedal animal reached a length of roughly 13 meters and tipped the scales at an estimated 9 tons, edging out the infamous Tyrannosaurus rex by a meter in length and some 3 tons in weight, says Coria.

"We compared it to the biggest T. rex known, a specimen known as Sue. I think it was much heavier and ran slower than T. rex," Coria told Science News. He and Salgado describe the animal in the Sept. 21 Nature.

The 100-million-year-old Giganotosaurus was not closely related to T. rex, which lived 65 million years ago in North America. During the Cretaceous period, South America had no land connection to North America and had started to split off from Africa, circumstances that allowed its dinosaurs to evolve independently.

Whereas T. rex had developed a specialized skull, forelimbs, and pelvis, Giganotosaurus retained the more generalized features of its forebears, says Coria. It may have resembled an oversized version of the well-known North American genus Allosaurus.

"The new find is adding information to our understanding of the late Cretaceous dinosaur faunas, and we have had a very North-America-centric view of what dinosaur life was like in the Cretaceous," says paleontologist Paul C. Sereno of the University of Chicago.

Giganotosaurus is one of a string of newfound carnivorous dinosaurs, or theropods. Last year, Sereno described an 8.2-meter-long early Cretaceous theropod from the Sahara Desert of Niger (SN: 10/15/94, p.245). This year, he discovered two late-Cretaceous theropods from the Moroccan Sahara. The larger one approached T. rex in size but probably did not equal Giganotosaurus.

The emerging theropods are forcing paleontologists to revise theories about how dinosaurs evolved in the separated Cretaceous lands. "These discoveries in South America, Africa, and other places are showing us there was quite a diversity of things happening on these continents. Now we have completely independent, huge predators that are competing with T. rex as the largest theropods," says Sereno.